An independent mental health hospital run by the Priory Group has been rated inadequate by the health watchdog.
Hertfordshire's Kneesworth House was downgraded from good by the Care Quality Commission (CQC) after it highlighted serious concerns.
The hospital, in Royston, specialises in acute mental health for over 65s, patients with learning disabilities and those at risk to themselves or others.
A spokesman said some aspects had been rated as good in the inspection report.
The CQC's deputy chief inspector of hospitals, Dr Paul Lelliott, said inpatient or secure wards were of most concern.
Hospital staff sometimes denied patients access to certain parts of these wards, cancelled patients' leave or cancelled ward activities because of a shortage of staff.
"We found three instances where staff had not recorded the justification for secluding patients for a prolonged period," he said.
"This was a concern when we last inspected the hospital in 2017.
"Seven patients that we spoke with told us that a few staff were rude, unfriendly and did not listen to them or antagonised patients."
Clinic rooms were also found to be disorganised and some wards dirty, according to the report.
"All of this is unacceptable and not what anyone should expect when receiving mental health care," the CQC said.
A Kneesworth House spokesman said it was important to note the report also rated the acute mental health and rehabilitation services "which make up the greatest proportion of beds, as 'good' and that overall the hospital was rated as 'good' for being effective and responsive".
The hospital has been placed in special measures following the inspection and will be re-inspected within six months.